Packaged foodstuffs, medicines, and the like can be contaminated during processing. Accordingly, they are often treated subsequent to the packaging operation to reduce spoilage. For some products which are especially susceptible to spoilage, these processes include sterilization, pasteurization, and the like. These processes are often performed in retorts under elevated conditions of heat and temperature for specified, often prolonged periods of time.
Where it is desirable to provide packaging in the form of rigid containers, it is often desirable to seal the package with a membrane or film. This membrane serves several purposes. It prevents tampering and pilfering of the container's contents. It assures continued cleanliness of the container's interior as well as the contents therein. Moreover, it can prevent gases, such as oxygen, from entering the package. Finally, it can serve as a label to identify and market the manufacturer's product.
One commonly practiced method for implementing such a sealing membrane is to provide one surface thereof with a sealing resin which can be adhered to the rigid container during processing. Such resins must be approved for direct food contact. The membrane is bonded to a rim about an opening on the container by activating the resin, often by means of heat. One methodology for providing this bonding heat is by induction sealing.
Induction sealing is generally performed by an inductive coil inside a sealing apparatus. The coil creates an electromagnetic field when it is energized by an electric current. The electromagnetic field causes an aluminum foil layer disposed in the lidstock to heat. This heating causes a resin coating, generally applied to the foil, to melt and adhere to the lip or rim of the container opening, thereby forming a seal between the lidstock and the container. When the container leaves the electromagnetic field, the foil cools, and the seal between the lidstock and the container is completed.
Early closure membranes required the user to cut into the membrane to open the container. For reasons of consumer convenience, it is now often desirable that such membranes be readily peelable from the container in order to provide access to the material stored therein. Examples of such implementations include, but are not limited to, dietary supplements, single serving convenience foods, and the like.
The foregoing examples of peelable lidstock membranes further illustrate a problem with existing technology. Where a peelable lidstock is utilized to package many foodstuffs, including adult dietary supplements, baby formula, and the like, an especially high degree of seal reliability is required. This is due to the fact that many such foodstuffs serve as excellent culture media for spoilage and pathological microorganisms, and infants and the elderly generally have lessened resistance to infection. To ensure that a healthy product is produced, many such foodstuffs are heat-treated in retorts subsequent to filling and sealing. With existing technologies, the heat used in retorting the packaged product often leads to softening of the sealing resins with concomitant loss of seal integrity and higher seal failures. In at least one application, the maximum acceptable failure rate is three failures per million containers.
A further problem with existing retortable lidding membranes is the removal thereof from the containers to which they are applied. The typically encountered induction sealed membrane is often substantially equal in form and size to the container to which it is applied, and is generally not substantially larger than that outer diameter. Accordingly, it is usually somewhat awkward to remove such membranes, as there is often no substantial “handle”, or removal feature, to remove the membrane.
One possible solution to this latter problem was the development of asymmetrical membranes, where the asymmetry provided a tab which extended substantially beyond the rim of the container, providing the requisite “handle” for removal of the membrane. An example of this methodology is the use of oval membranes over round openings. The problem with using this methodology in induction sealed membranes is that the induction energy used during the sealing process tends to follow the rim of the foil and not along the mass of the container rim. Accordingly, the energy available for sealing is substantially diminished at the container/seal juncture in the region of the asymmetry. While not wishing to be bound by theory, it is believed that this leads to increased seal failures at the region of asymmetry, with concomitant increases in product leakage and spoilage.
Accordingly, it would be desirable and useful to provide a heat-sealable, peelable lidding membrane suitable for retort packaging.
It would be further desirable and useful to provide a heat-sealable, peelable lidding membrane suitable for retort packaging which incorporates an easy removal feature therewith.